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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54022
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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My check engine light is on and my gas cap loose message is

Customer Question

My check engine light is on and my gas cap loose message is on?
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.

Hi, my name is***** the gas cap is fitted properly the message would be indicating that a large leak has developed in the fuel tank evaporative system. A loose or missing gas cap is the most common cause of a large leak but you could also have a faulty vapor canister shut off valve or purge valve or there could be a leak at one of the vapor hoses. If you have checked the gas cap and it was not fitted properly, refitting the cap will take care of the problem and the check engine light will turn off in a few days. If no fault was found with the fuel cap you will need to have a fuel system evaporative system test performed to check for leaks in other parts of the system.

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